Various golf balls, golf ball layers, and methods of making golf balls are generally known in the art. The centers may be fluid-filled or solid. Such golf balls may have a multilayer construction having one or more wound and/or solid layers. Golf balls may comprise one-piece constructions or they may include several layers including a core, one or more intermediate layers and an outer cover that surrounds any intermediate layer and the core.
Regardless of the form of the ball, players not only seek a golf ball that embodies a beneficial combination of properties, for example, such as maximum distance, which requires a high initial velocity upon impact, but they desire golf balls that are aesthetically and cosmetically free from defects. It is especially desirable to manufacture a golf ball having covers that are aesthetically and cosmetically free from defects as the cover is the outermost component visible to golfers.
Golf balls are typically manufactured by various molding processes, whether one-component or multi-component balls. The cover is then formed over the core and intermediate boundary layers, if present, through casting, compression molding, and/or injection molding.
The cover is typically made from any number of thermoplastic or thermosetting materials, including thermoplastic resins such as ionomeric, polyester, polyetherester or polyetheramide resins; thermoplastic or thermoset polyurethanes or polyureas; natural or synthetic rubbers, such as balata (natural or synthetic) or polybutadiene; or some combination of the above.
Polyurethanes have also been recognized as useful materials for golf ball covers since about 1960. The resulting golf balls are durable, while at the same time maintaining the “feel” of a balata ball. Because the polyurethanes used to make the covers of such golf balls generally contain an aromatic component, e.g., aromatic diisocyanate, polyol, or polyamine, they are susceptible to discoloration upon exposure to light, particularly ultraviolet (UV) light. To slow down the discoloration, light and UV stabilizers, e.g., Tinuvin 770, 765, and 328, are added to these aromatic polymeric materials. However, to further ensure that the covers formed from aromatic polyurethanes do not appear discolored, the covers are painted with white paint and then covered with a clear coat to maintain the white color of the golf ball. Polyureas have also been proposed as cover materials for golf balls. For instance, a polyurea composition comprising the reaction product of an organic diisocyanate and an organic amine, each having at least two functional groups, is known.
Conventionally, castable aromatic polyurethane elastomers have been molded using molds that are preheated between 140° F. to 180° F. and cores that are preheated between 100° F. and 140° F. Such preheating is thought to facilitate a reasonable gel time to allow cores to be centered into the castable material and the cover to be molded over the cores. Golf balls molded from preheated cores also help to reduce seam failures at the time of demolding because of reduced core expansion rate of the preheated cores during molding. However, casting aliphatic polyurethane and polyurea elastomers under such conditions is problematic, particularly because of the formation of surface defects. Balls typically molded with preheated cores and/or preheated molds to these temperatures result in voids and blisters.
Accordingly, there is a need for a method of molding cosmetically defect free golf ball components that are comprised of aliphatic polyurethane elastomers or aliphatic polyurea elastomers. The methods of the present invention provide for such a method.